A common misconception about veterinary professionals is that we play with puppies and kittens all day. The reality is that very little of our time is spent snuggling adorable little pets. However, you will have those awesome appointments when you get to meet a family’s recently adopted kitten.
It’s usually a long appointment discussing feeding, handling, litter box care, parasite prevention, spaying or neutering, and vaccination schedules. Typically it ends with ridiculous amounts of baby talk and playing with the kitten. Imagine the horror when 4 weeks later, instead of coming in for a vaccination booster, the kitten presents with a decreased appetite, increased respiratory effort, abdominal fluid and a fever.
Feline infectious peritonitis (FIP) is a frustrating and tragic disease. It is frustrating because it is a difficult disease to definitively diagnose. A post mortem is the gold standard. It is tragic because once the disease has taken hold there is really nothing that you can do for your patient other than make him or her comfortable until euthanasia. FIP is caused by a feline enteric coronoavirus (FECV).
The virus lives in the intestines and is shed in the feces. It is most commonly transmitted via the fecal oral route from simple grooming and co-housing. In its original form FECV causes mild self-limiting diarrhea or no clinical signs at all. The disease prevalence is 40% to 90% depending on population density. We only see FIP when the virus mutates and luckily this mutation occurs very rarely only in 5-10% of cats.
Scientists do not yet understand what causes the mostly innocuous coronavirus to mutate in the deadly FIP virus. Once FIP has mutated it is able to replicate in monocytes and macrophages. These monocytes and macrophages distribute throughout the body where the virus is free to invade other tissues. FECV is considered highly contagious but FIP does not appear to be regularly transmitted from patient to patient.
There are two forms of FIP: wet and dry. Most of the time the clinical signs are vague like decreased appetite, decreased activity, weight loss, and intermittent fever. These patients do not improve with antibiotics. Not exactly a slam dunk list of clinical signs.
How Will I Know if a Cat has FIP?
You’ll start to be suspicious for FIP when you have a vaguely sick young cat, especially if that young cat lives in a cattery, shelter or multiple cat household. Oftentimes there is a stressful event like adoption that predates the arrival of clinical signs by 4-6 weeks. The wet or effusive form generally causes acute illness. Due to vasculitis fluid builds up in the thoracic and abdominal cavities. Noneffusive or dry FIP may occurs over months to years and the clinical signs vary based on the organs involved, but pyogranulomatous lesions can be found throughout the body.
You can screen cats for coronavirus with antibody testing but this does not tell you if the virus has mutated and can only be used to rule out FIP as a likely diagnosis. In order to diagnose FIP in a sick cat, you will have to be aggressive with your diagnostics and piecing together the clinical signs. On the CBC you may see lymphopenia, neutrophilia, anemia, or thrombocytopenia.
Hyperproteinemia is the most common chemistry abnormality you will see. Yellow fluid (modified transudate) in the thoracic or abdominal cavity is a big clue for the wet form of FIP. The gold standard for diagnosis is examination of affected tissues, obtained by biopsy or on post-mortem examination.
Treatment for this disease is only palliative as it is ultimately fatal. Prednisone to suppress the immune system can be attempted with variable results. There are new biologics being tested and hopefully future patients will benefit from this emerging technology. An FIP vaccination is available but is not recommended by the American Association of Feline Practitioners due to lack of efficacy.
In conclusion, FIP can be tricky to diagnose and unfortunately ends in a sad situation. Keep it on your differentials list.
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